im not on trt, but on cycle i love hitting sholders and ass, 25g sholders and 23g ass, its not hard to acctually pin the ass bro cos ur going for the top outer quorter of the ass cheek, if u search on youtube u will be able to find videos that will help u out. and u might be hitting a vain cos ur not puting the pin alll the way, if u are than draw a little on the plunger of the syringe if u get blood into it that means u hit a vain so just pull it out and put it somewhere else.